1. Technical Field
The following description relates to one or more techniques to correct a positional deviation of an image to be formed by an image forming device.
2. Related Art
An image forming device such as a color laser printer has been known, which includes a plurality of image forming units aligned along a sheet carrying belt such that toner images of respective different colors are sequentially transferred onto a sheet being conveyed on the sheet carrying belt by the image forming units. In such an image forming device, when the respective toner images are transferred in different positions on the sheet by the image forming units, an image is formed as a low-quality one.
In order to ensure the quality of the image, a technique referred to as registration to correct positional deviations between the toner images transferred onto the sheet has been employed (for example, see Japanese Patent Provisional Publication No. HEI8-118737). According to such a correction technique, a pattern that includes a plurality of marks is formed on a surface of the sheet carrying belt by each image forming unit, and the positional deviations between different color toner images are measured by detecting locations of the marks with an optical sensor. Then, based upon a result of the detection, the positional deviations between the toner images are corrected. It is noted that the measured deviations may periodically fluctuate due to unevenness in thickness of the sheet carrying belt. In general, the patterns are formed throughout a circuit of the sheet carrying belt. The positional deviations of the marks included in the pattern are measured in a plurality of locations on the sheet carrying belt, and the positional deviation correction is performed based upon an average value of the measured deviations.